Metastable beta titanium-base alloy

ABSTRACT

A metastable beta titanium-base alloy in which beta stability is achieved by optimum addition of beta-eutectoid element (iron, manganese, chromium and/or cobalt). Also included are betaisomorphous elements (vanadium and/or molybdenum), aluminum, and optionally one or both the neutral elements (tin and zirconium). Alloy is readily formable at room temperatures and can be heattreated to high tensile strength.

United States Pateni [72] inventors Howard B. Bomberger, Jr.

Canfield; Stanley R. Seagle, Wurr an; Ronald R Seeley, C infield, all of 0111;. [2]] Appl. No. 764,585 {221 Filed Oct. 2, 1968 [451 Patented Oct. 26, 1971 {73] Assignee Reactive Metals, Inc,

154] METASTABLE BETA TITAMUM'BASE ALLOY 8 Claims, 2 Drawing Figs.

[52] U.S.Cl v U 7 75/1755 [51] lnLCI 4C22c1$/01l 150] Field Search... i a a 7. 75/1 5 5, 148/32 1 N [56l References Cited UNITED STATES PATENTS 2,596,485 5/1952 Jafi'ee el al .1 5/1755) Filler Jaffee et a1...

Jaffee et a1 w. Kessler et al....

Vordahl Vordahl Jaffee etal i. Vordahl .lal'fee et al Primary Examiner-Charles N Lovell ilslomey- Walter P, Wood 75/1755 75/1755 IS/175.5 75/175.5X 75/1755 75/1755 75/1755 75/1755 X 75/1755 X ABS'IRACT: A metastable beta titanium-base alloy in which beta stability is achieved by optimum addition of bela-eutectoid element (iron, manganese, chromium and/or cobalt). Also included are beta-isomorphous elements (vanadium and/or molybdenum), aluminum, and optionally one or both the neutral elements (tin and zirconium). Alloy is readily 10111131712 at room temperatures and can be heat-treated to high tensile strenglh.

TEMPERA TURE PATENTEDUDT 2s IQTI TEMPERA TURE F.

Alpha Alplm+8efa Fl'hl- Be Ia +Compound A lpha Compound A TOM/C PERCENT BETA-ELITECTOID ELEMENT TYPE-=2- Cr Fe l L I l l l ATOM/C PERCENT BETA-EUTECTOID ELEMENT IN VEN TORS. HOWARD B. BOMBERGER JR., STANLEY R. SEAG'LE and RONALD R. .SEELEY A r rarney METASTAILE BETA TITANIUM-BASE ALLOY This invention relates to an improved high-strength metastable beta titanium-base alloy.

Titanium-base alloys used for structural purposes in the aircraft and aerospace industries should possess several important characteristics. The alloy should be produced readily as a mill product, such as sheet, strip, plate, bar, billet, tubing or wire, by melting, forging, rolling or other commercial metalworking processes. Preferably final production and fabrication of sheet, strip, tubing and wire are performed at room temperature for reasons of efficiency and economy and to attain a desirable surface finish and properties. in its annealed or softened state the alloy should have sufficient ductility (l percent minimum elongation in 2 inches) to allow considerable forming at room temperature. It should be possibk to bend a sheet of the alloy to a radius less than twice its thickness without breaking the sheet. The least radius to which a sheet can be bent is referred to as its minimum bend radius" (MBR) and is usually expressed as a ratio of radius-tothickness. The alloy should respond to heat treatment and achieve heat-treated yield strengths greater than I60 Ks.i. with useful toughness and ductility (4 percent minimum elongation in 2 inches), which properties it should retain afier prolonged exposure to temperatures up to 600" F. under allowable design stresses. The alloy also should have high strengthto-weight ratios which are needed in weight-critical structures.

It is well known that titanium metal may exist as an alpha phase, a beta phase, or an alpha-beta structure which is a mixture of the two phases. At room temperature the pure metal assumes the alpha phase, which has a closely packed hexagonal crystalline structure. On heating above the beta transus temperature (about 1,625 F.), the pure metal assumes the beta phase, which has a body-centered cubic crystalline structure. The beta phase can be retained wholly or in part at room temperature by adding to titanium certain alloying elements known as beta stabilizers. These may be either beta-eutectoid elements, such as iron, manganese, chromium, cobalt or nickel, or beta-isomorphous elements, such as vanadium, molybdenum, columbium or tantalum. Usually the alpha phase has greater mechanical strength than the beta phase, but less ductility. The alpha-beta structure represents a compromise which affords both the strength and ductility needed for many applications.

Most previous attempts to meet the requirements hereinbefore stated have involved the use of alpha-beta alloys, which usually are processed at high temperatures with little cold reduction possible between annealing and cleaning treatments. High-temperature metalworking often necessitates an expensive surface cleaning operation of the product after it has been hot-worked or formed. These alloys are limited to moderate yield strength ranges of [20 to I50 Kai. with limited ductility and toughness.

An object of our invention is to provide a metastable allbeta titanium-base alloy which possesses the desirable characteristics hereinbefore listed.

A further object is to provide an alloy which has these characteristics and can be produced with conventional mill equipment and is sufficiently ductile to be cold-worked and finished at room temperature, yet can be simply heat treated to medium and high strengths.

A further object is to provide an alloy of the foregoing characteristics in which we control the average valence electron density (VED) to a critical range (about 4. i 5 to 4.30).

In the drawing:

FIG. 1 is a typical phase diagram of a titanium-beta-eutectoid element system; and

F IG. 2 is a graph illustrating how we determine the theoretical maximum content of beta-eutectoid elements in our alloy.

Our alloy contains one or more of the beta-eutectoid elements iron, manganese, chromium or cobalt. These elements have advantages for stabilizing the beta phase of titanium alloys, since they are compatible with the melting process (no master alloys required), they are relatively lightweight compared with the beta-isomorphous elements, and they are strong beta stabilizers. However, if they are added to a titanium alloy in excessive quantities, compounds form and ductility is lost. Preferably we include in our alloy beta-eutectoid elements near the maximum quantities that do not form compounds. We look to the phase diagrams to determine the content we can safely include.

As FIG. I shows, some known percentage of a beta-eutectoid element added to titanium forms a eutectoid at some known temperature, indicated at point b. The percentage and temperature of course are different for each beta-eutectoid element, but all follow a similar pattern. Line a-b represents the boundary between the beta phase and the beta-plusFcompound. We extrapolate line 0-1: to 752 F. to determine the theoretical maximum content of the element which can be included at this temperature without forming a compound, indicated at point e. Similarly we extrapolate the line to room temperature (approximately 50 to I00 F.) to determine the maximum at room temperature, indicated at point d.

FIG. 2 shows the extrapolation for the five beta-eutectoid elements iron, manganese, chromium, cobalt and nickel. The extrapolated curves for the first four reach room temperature at atomic percentages of the element ranging from about 3.5 to 8.5, but the extrapolated curve for nickel never reaches room temperature. Hence we may use any of the first four elements, but not nickel, as beta stabilizers in our alloy. We limit the content of beta-eutectoid element in our alloy to the maximum established by extrapolation of the curves to room temperature. in this manner we arrive at the following content for each element when used individually:

Atomic Percent lron Up to 4.5% Manganese Up to 6.0% Chromium Up to 8.5% Cobalt Up to 3.5%

Atomic Percent Vanadium 1 to 16'! Molybdenum l to 6% Columbium 3 to 235 Tantalum 3 lo 21% The betadsomorphous elements thus supplement the beta-eutectoid elements in stabilizing the beta phase in our alloy. We presently prefer vanadium and molybdenum because of their lower cost and greater efficiency as beta stabilizers.

Our alloy also contains aluminum in proportions of about L75 to 7 atomic percent. We use aluminum as a strengthening agent. Usually aluminum is an alpha promoter and inhibits retention of the beta phase at room temperature. We overcome this effect of aluminum in our alloy by our inclusion of large quantities of beta-eutectoid and beta-isomorphous elements already described.

Our alloy also may contain at least one of the neutral elements tin and zirconium in the following approximate proportions:

3 4 Atom: "FPF, The preferred composition ol alloyis within the following approximate range (excluding incidental impurities): 1 51 3:: :1: Atomic Percent 5 The neutral elements improve the ductility of our alloy and re- 2 tard formation of an undesirable brittle omega phase. v 4 m We have found that a necessary condition for a titaniumm 1.5 w as base alloy to retain an all-beta structure at room temperature m 2' z is that it have an average valence electron density (VED) T above 4. usually at least 4.15. To calculate the average VED of an alloy, the atomic percent of each element is multiplied by of valence f and sum of 5 Specific nominal compositions which we have found adproducts is divided by 100. Titanium itself has 4 valence elecvanmseom are as mum" in ammic percent.

trons, as have the neutral alloying elements zirconium and tin. Aluminum has 3 valence electrons, and as already mentioned is an alpha stabilizer, which retards formation of the beta phase. The heta-isomorphous elements vanadium, columbium 2.5% Fe or 3.595 H1: or 5.55 Cr or and tantalum have 5 valence electrons while molybdenum has 122: 6. The beta-eutectoid elements which we can use have valence m-za electrons as follows:

- r Ti- Balance $2 .7 Preferably we add to any of these latter compositions tin chromium 6 and/or zirconium in amounts of approximately L5 to 2.5 percob-n 9 cent of the alloy.

In the tables which follow, we show the properties of a number of specific alloys. The first three alloys listed in table I The calculation of the VED of a titanium-base alloy is given by fall outside our invention, while the others are within. Alloy l the following equation using atomic percentages: has a VED below our critical range and its MBR is much too VED-0.04(%Ti-t-ZR+N H-0.07(%Mn)+0.06(%Cr-l-%Mo)-lhigh. Alloys 2 and 3 have VED at or above the upper limit of 0.08(%Fe)+0.09(%Co)+0.05(%V+%Cbl-%Ta)-0.03(%A1) our critical range. While they meet bend requirements. aging Our alloy has a VED of 4. 15 to 4.35, which we regard as critiproduces no significant increase in their hardness or tensile cal as demonstrated hereinafter by actual examples. gtrfr gtlL TABLE I.PROPERTIEB OF METAHTABLE BETA-TITANIUM ALLOY SHEET 2? Composition, atomic percent VED Heat treatment 1 53: K32: PEMEHIEI 5:13:21: lliififiilj3 3i5152:13:23?"'"Iiiiiiitiiji: {if} l$fi$l3iiiiiiji Z? a 'naz, Mo-8.1,V-6.5,Mn-l.7, Sn 4. 35 +900 Fm hL-AC g 4 Ti-2.0, Brio-7.8, v-4.4, tin-1.4. .41 4.20 g; 'Ii-BJ, Mo-1.o,v-2.a,re-a.4,.41 4.19 557; a Ti-ll.1,Mo-7.7,V-6.6, 01-41 11 4.21 1 1; 7 Ti-3.1,Mo-7.6,V-3.5,Mn-ll.4,Al 4.19 4 43 s '1'1-2.1, Mo-7.8, v4.5, l e-3.3, zhu, Al 4.24 an n T1-2.1,Mo-1.9, V-LB, l e-11.7, nan-2.5, smut, Al 4. 25 g 10 Tl-2.0, MO-7.5,V-6.6, (Jr-6.2,Al 4.16 66 11 Ti-1.7,Mo-7.6,V-3.6,Mn-5.3,Al 4.11

12 TH, Mo-2.s,Mn-1.7,sn-4.a,1u 4.17

13 '11-a.1, bio-2.0, v-1.s, I e-11.6, 1111413, 2145.41, A1 4.21

14 Ti-3.l, Mo-7.a,v-2.o, Co-6.l5,Al 4.19

TABLE IL-PBOPERTIES OF HIGH STRENGTH TITANIUM ALLOYS Composition, atomic percent Density, Heat UTS, El lbJeu. in. treatment Kai. Yr, Kai. percent Ti-iLl, lilo-7.7, if-8.6, Lin-6.4, Al 0. 8'1 126 122 16.8 STA 1118 184 5. 8 Ti-3.1, hie-7.8, V-3.6, bin-2.1, 2141.15, A] 0. 172 ST 134 182 12.0 STA 200 187 7.5 Pi-3.0, lilo-7.6, V4.7, Cr-BA, Al 0.171 ST 121 112 11.5 STA 195 179 7.0 Pl-2.0, lilo-7.6, V-6.fl, (Br-6.4, AL 0.169 ST 121 116 14.8 STA 191 176 8.5 Ti-3.0, Mo-Lti, V4.5, Lin-7.2, A1 0.170 5'! 132 127 13. 8 STA 803 186 6. 6 Ti-LB, bio-7.7, V4.6, Mil-1.6, Sn-ll.4, Al 0.171 ST 129 124 13.0 STA 204 189 6.1) Tl-2.0, bio-7.6, V2.7, l e-6.5, Al 0.170 8'! 121 113 13. 5 STA 173 7.2

l S'l=Solution- Treated; 8 IA=Solutlon-Treated and Aged. V

TABLE III.--STABILITY OF HIGH STRENGTH TITANIUM ALLOY Before creep After creep Composition, atomic percent Kai Ks.i. percent Creep exposure Ks.l. K81 percent CPI-3.1, M'7.7, V 3.6, Mn-A, Al 198 134 5. 8 600 F.-1l6 Ks.i.-96 hr 197 189 6 8 Ti-al, Moms, Vac, Mil-2.1, Zr-5.5, A1,. 205 192 199 190 0. 0

Ti-3.o, Mir-7.6, V4.7, (Zr-5.4, A) 195 179 201 192 4. 5

Ti-zo, Mo-7.6, V415, (Ir-5.4, At... 174 153 117 160 0. 5

T1410, Mo-7.6, 3.5. Mir-7.2, A1 202 182 196 171 4. 3

Ti-ao, Mo-7.6, V-aa. Mil-7.2, Al 202 132 194 172 6.5

Ti-Lfi, M0-7.7, V4.5, Mn-l.6, Sn-5.4, A 206 190 198 179 6.5

We Claim: amount of approximately 2.5 percent of the alloy. Mn in the l. A metastable beta titanium-base alloy which consists esamount f appmximatdy 3 5 percent f h anoy C i h sentla y 0 5 amount of approximately 5.5 percent of the alloy, and Co in a. at least one beta-eutectoid element selected from the group which consists of iron, manganese. chromium and cobalt in a maximum content determined by the equation:

b. 4 to 9 percent vanadium,

c. L5 to 3 percent molybdenum,

d. 3.5 to 7 percent aluminum,

e. balance titanium and incidental impurities. the foregoing quantities being in terms of atomic percentages, said alloy having an average valence electron density of about 4. to 4.35.

2. An alloy as defined in claim 1 containing in addition at least one neutral element selected from the group which consists of tin and zirconium in amounts up to approximately 3 percent of the alloy.

3. An alloy as defined in claim 1 in which the beta-eutectoid element is selected from the group which consists of Fe in the the amount of approximately 2.0 percent of the alloy, the remainder of the composition being approximately as follows:

V 7.5% Mo 2% Ti Balance.

4. An alloy as defined in claim 3 in which the beta-eutectoid element is iron.

5. An alloy as defined in claim 3 in which the beta-eutectoid element is manganese.

6. An alloy as defined in claim 3 in which the beta-eutectoid element is chromium.

7. An alloy as defined in claim 3 in which the beta-eutectoid element is cobalt.

8. An alloy as defined in claim 3 containing in addition at least one neutral element selected from the group consisting of tin and zirconium in amounts of approximately 1.5 to 2.5 percent of the alloy.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 615 378 Dated October 1971 Howard B. Bomberger, Jr., et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 34 "ZR" should read Zr same line "N" should read Sn line 35, the minus sign preceding "0 .03 Al) should read Column 4, Table I under "MBRM R/T" first line should read 25 Signed and sealed this 21st day of November 1972.

(SEAL) Attest:

EDWARD I I.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents v1 PO-10 0 USCOMM-DC 60376-F'69 fi U.S GOVERNMENY PRIN ING OFFICE: "II O-JG-JJL 

2. An alloy as defined in claim 1 containing in addition at least one neutral element selected from the group which consists of tin and zirconium in amounts up to approximately 3 percent of the alloy.
 3. An alloy as defined in claim 1 in which the beta-eutectoid element is selected from the group which consists of Fe in the amount of approximately 2.5 percent of the alloy, Mn in the amount of approximately 3.5 percent of the alloy, Cr in the amount of approximately 5.5 percent of the alloy, and Co in the amount of approximately 2.0 percent of the alloy, the remainder of the composition being approximately as follows: V 7.5% Mo 2% Al 5.5% Ti Balance.
 4. An alloy as defined in claim 3 in which the beta-eutectoid element is iron.
 5. An alloy as defined in claim 3 in which the beta-eutectoid element is manganese.
 6. An alloy as defined in claim 3 in which the beta-eutectoid element is chromium.
 7. An alloy as defined in claim 3 in which the beta-eutectoid element is cobalt.
 8. An alloy as defined in claim 3 containing in addition at least one neutral element selected from the group consisting of tin and zirconium in amounts of approximately 1.5 to 2.5 percent of the alloy. 